This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. At present, current immunoassay methods cannot accurately or precisely measure low levels of steroid hormones in humans. As a result, below a certain lower limit of detection using conventional laboratory methods, testing for steroid levels in the blood often yields little clinically useful information. Postmenopausal women and women who have had their ovaries removed who are being studied for androgen replacement need an accurate method of monitoring treatment. Children who have clinical signs of precocious puberty need a method of measuring low testosterone or estradiol levels that may support clinical findings and are different from the levels of normal children. However, levels in normal children cannot be accurately measured because of the inherent problems of the current assay methods Tandem mass spectrometry (aka liquid chromatography-mass spectrometry-mass spectromery or LCMSMS) has the potential to sensitively, accurately, and precisely measure low levels of hormones. The Harbor-UCLA General Clinical Research Center would like to validate measurement of androgens, estradiol, steroid metabolites, and synthetic steroid compounds using tandem mass spectrometry. In order to validate measurements using tandem mass spectrometry, samples of human serum are needed. We propose to use leftover blood from patients whose clinical information is known and are having clinically indicated laboratory testing as ordered by his or her regular physicians. The volume of blood needed from each sample is approximately 200 ul.